On Friday, Russian President Vladimir Putin completed his move to annex four more regions in Ukraine, defying international law and several warnings by the United States and its allies.

The annexation, which involves Donetsk, Luhansk, Kherson and Zaporizhzhia, was cemented in a grand ceremony held at the Kremlin – which was followed by a rally graced by “patriotic” Russians.

During the ceremony, Putin declared that the four partially occupied regions of his neighbor’s south and east were joining Russia forever, and that he would use all means to protect them.

“They will become our citizens forever,” Putin told officials at the Kremlin ceremony. “We will use all means available to us to defend our lands,” he said.

This comes after a referendum, which has been widely described as sham, was conducted in the regions. Pro-Russia residents of the regions were said to have voted in favor of the annexation.

Putin handed Moscow-installed leaders signed annexation documents on Friday. He demanded Ukraine stop fighting and begin talks, but ruled the territories out of any negotiation.

The United States, in response to the annexation, swiftly imposed “swift and severe costs” new round of sanctions against Russian government officials, bankers and military suppliers.

“The United States condemns Russia’s fraudulent attempt today to annex sovereign Ukrainian territory,” President Joe Biden said in a statement. “Russia is violating international law, trampling on the United Nations Charter, and showing its contempt for peaceful nations everywhere.”

Biden added that the US “will rally the international community to both denounce these moves and to hold Russia accountable.”

The United Nations also denounced the annexation, calling it illegal. In his response, Ukrainian President Volodymyr Zelenskiy condemned the annexation, rejecting Putin’s call for dialog. He said Dialog “is impossible with this Russian president,” and vowed to press ahead with his counteroffensive.

The European Union is also planning to impose its own sanctions. In a statement on Friday, the union said they “reject and unequivocally condemn the illegal annexation by Russia” which not only violated Ukraine’s rights, but also put “global security at risk.”

The latest development may introduce a new phase to the conflict. President Volodymyr Zelenskyy announced that he was submitting his country’s formal application to join NATO, praying for swift acceptance by the Western military alliance that has many other European countries as members.

NATO defends the territory of its members, setting up a potential escalation of the war if Ukraine joins the alliance. Kyiv has wanted to join the alliance for years, as it would give it the protection of collective defense that the members have.

However, accelerated accession of NATO’s membership at this time is highly a doubt. The US Secretary of State Antony Blinken said “we strongly support NATO’s open doors, we strongly support bringing into NATO countries that seek to join and that can add to NATO’s capabilities. There’s a process for doing that and countries will continue to follow that process.”

The challenge lies on Zelenskyy’s request to fast-track Ukraine’s membership. It takes several months for the application for NATO’s membership, which must be vetted by the alliance members, to be approved.

Ukraine isn’t the only European country seeking to join NATO in the wake of the war. Sweden and Finland had earlier applied, but are still waiting for rectification by all members.

On the other side of the conflict, Ukraine is increasingly recovering captured territories from Russia, questioning the Kremlin’s ability to protect the annexed regions.

The US and its allies have vowed to continue to supply Kyiv with ammunition and other aids to defend its territory. Earlier in September, the Kremlin announced partial mobilization of 300,000 men to reinforce its depleted army. That and Putin’s threat to deploy nuclear weapons are seen as pointers that Russia currently lacks the military strength to defend the annexed region from the fortified advancing Ukrainian army.